Multiple beam antennas form a plurality of communication beams. Communications satellites typically employ multiple beam antennas that have one or more feed elements feeding a reflector or a lens.
Multiple beam antennas usually have feed element groups that overlap, whereby a feed element is driven to generate a component beam that is combined with component beams from other feed elements to form a composite beam, or communications beam. A low-level beam forming network within the communications satellite controls the interaction of feed elements.
Conventional beam forming networks that generate multiple beams from a feed array describe planar dividers and combiners connected by individual connections having equal propagation delays. However, equal propagation delays are not always desirable. In some applications it is desirable to choose different propagation delays or phase shifts in order to improve the performance of the composite beam formed from the component beams.
For example, when the focal length of a reflector or lens antenna is relatively short compared to the aperture diameter, there may be phase and amplitude errors in the resulting aperture distribution for beams not near the antenna boresight. In such cases, it is desirable for the amplitude and phase of the beam-forming network to be adjusted to compensate for these errors.
Another example where adjustable beams are desired is in the case of an array built on a planar surface, as opposed to a spherical surface. An array on a planar surface significantly reduces the manufacturing and assembly costs. However, it introduces the need for selectable amplitude and phase weights for each beam to optimize the antenna's performance. Individually weighting the contribution from each beam compensates for the aberration caused by building the feeds on a planar surface.